var base64Str = 'emhhbmdzYW46MTIzNDU2';
var buf = Buffer.from(base64Str, "base64");
var str = buf.toString("utf-8");
console.log(str);
var arr = str.split(":");
var str1 = "用户名:" + arr[0] + "密码:" + arr[1];
console.log(str1);